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I want to create an environment that receives an argument and an optional argument in such a way that the first argument will be a title and the optional argument will decide whether the title should be justified to the left or centered. It's possible without any package?

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  • 1
    Yes, this is possible and there are many packages, that provide such environments already, e.g. mdframed or tcolorbox, with lot of additional features.
    – user31729
    Feb 1, 2019 at 17:25
  • You should take look at the xparsepackage to do that.
    – Bernard
    Feb 1, 2019 at 17:26
  • I want to do it without any package.
    – Joan
    Feb 1, 2019 at 17:29

3 Answers 3

Reset to default
5

The optional argument can be l or c (default c).

\documentclass{article}

\makeatletter
\newenvironment{something}[2][c]
 {\begin{\csname #1@somethingtitle\endcsname}
  \bfseries #2
  \end{\csname #1@somethingtitle\endcsname}}
 {\par\addvspace{\topsep}}
\newcommand\l@somethingtitle{flushleft}
\newcommand\c@somethingtitle{center}
\makeatother

\begin{document}

\begin{something}{This is centered}
This is the environment's contents
This is the environment's contents
This is the environment's contents
This is the environment's contents
\end{something}

\begin{something}[l]{This is left flush}
This is the environment's contents
This is the environment's contents
This is the environment's contents
This is the environment's contents
\end{something}

\end{document}

enter image description here

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  • I would like to know why you use the char @?
    – Joan
    Feb 1, 2019 at 22:10
  • @Joan In order to avoid clashes with user macros.
    – egreg
    Feb 1, 2019 at 23:02
  • in the case that I want to add an optional argument that allows to decide if the title wants to be added to the ToC, how could I do it?
    – Joan
    Feb 21, 2019 at 21:04
4

enter image description here

Without any package: Using an optional argument that is checked with \pdfstrcmp (a pdftex primitive).

If #1 is equal to left, the title is left aligned, in any other case it is centered. 

\documentclass{article}

\newenvironment{foo}[2][]{%
  \ifnum\pdfstrcmp{#1}{left}=0%
  #2%
  \else
  \hfil#2\hfil%
  \fi%
  \medskip

}{}

\newcommand{\footitleformat}[1]{%
  \bfseries\MakeUppercase{#1}%
}

\newenvironment{fooother}[2][]{%
  \ifnum\pdfstrcmp{#1}{left}=0%
  \footitleformat{#2}%
  \else
  \begingroup
  \centering 
  \footitleformat{#2}%

  \endgroup
  \fi%
  \medskip

}{}



\begin{document}

\begin{foo}{This is centered}
  Foo stuff
\end{foo}


\begin{foo}[left]{This is not centered}
Other Foo stuff
\end{foo}

\begin{fooother}{This is centered again}

Yet another Foo stuff
\end{fooother}


\end{document}

\documentclass{article}

\newenvironment{foo}[2][]{%
  \ifnum\pdfstrcmp{#1}{left}=0%
  #2%
  \else
  \hfil#2\hfil%
  \fi%
  \medskip

}{}


\begin{document}

\begin{foo}{This is centered}
  Foo stuff
\end{foo}


\begin{foo}[left]{This is not centered}
Other  Foo stuff
\end{foo}


\end{document}
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11
  • I try to use {\centering\bfseries\MakeUppercase{#2}} but the text is not center...
    – Joan
    Feb 1, 2019 at 18:01
  • @Joan: You need an empty line after \centering
    – user31729
    Feb 1, 2019 at 18:04
  • Don't understand.
    – Joan
    Feb 1, 2019 at 18:13
  • @Joan: I changed the answer: I was too short in my explanation ... you need an empty line after the text that is to be centered.
    – user31729
    Feb 1, 2019 at 18:25
  • 1
    @Joan: See the answers to the question here -- it takes too long to explain this in a comment
    – user31729
    Feb 1, 2019 at 20:25
3

Write the environment to take a key-valued optional argument

enter image description here

\documentclass{article}

\usepackage{xkeyval}

\makeatletter
% From the xkeyval documentation (section 3.3 Choice keys)
% http://texdoc.net/texmf-dist/doc/latex/xkeyval/xkeyval.pdf
\define@choicekey*{paralign}{align}[\val\nr]{left,center,right}[center]{% Add align=? key-value
  \gdef\titlealign{}%
  \ifcase\nr\relax
    \gdef\titlealign{\raggedright}\or% 0 = left
    \gdef\titlealign{\centering}\or% 1 = center
    \gdef\titlealign{\raggedleft}% 2 = right
  \fi
}
\define@cmdkey{paralign}{format}[]{}% Add format=? key-value

\newenvironment{mytitle}[2][]{%
  \par\addvspace{\medskipamount}
  \begingroup
    \setkeys{paralign}{%
      align,format,% Default settings (align=center,format={})
      #1}% Local settings
    \titlealign \cmdKV@paralign@format #2%
    \par
  \endgroup
  \nobreak\smallskip
}{%
  \par\addvspace{\medskipamount}
}
\makeatother

\begin{document}

\begin{mytitle}{Centred titled}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus placerat 
enim ligula, a efficitur augue sodales non\ldots
\end{mytitle}

\begin{mytitle}[align=left]{Left-aligned title}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus placerat 
enim ligula, a efficitur augue sodales non\ldots
\end{mytitle}

\begin{mytitle}[align=right,format=\bfseries]{Right-aligned title}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus placerat 
enim ligula, a efficitur augue sodales non\ldots
\end{mytitle}

\end{document}
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